How long will my wort take to chill?

[djheater]

I just got done building an ice rink in the back yard and I needed to brew today too, but now I'm lazy and don't want to set up the IC and watch it, etc. It's 15 degrees out, and I packed snow around the kettle.

How long do you think it will take 5 gallons of sugary water to chill to 70 degrees?

I'm gonna give it 30 minutes and have a beer, maybe snap some pics of the rink.

Gratuitous ice rink photo.

 

[jorken]

cha?

 

[DrPizza]

Ah ha! This is the perfect time to apply Newton's Law of Cooling.

Assuming you knew the initial temperature, take the temperature now. (plus the outdoor temperature)

T = Ce^kt + R
where T is the temperature of what's cooling
R is the outdoor temperature
t = time
C = T-R (assuming you start timing at 0)

Plug in the current temperature & how many minutes (or do it in hours if you wish) since you first started cooling it. Solve for k.

Then, plug in the Temperature you're waiting for & solve for t

 

[DrPizza]

Incidentally, as geeky as it sounds, I used that formula while making summer sausage from venison the other day. I needed to know approximately how long until my sausage would reach 156 degrees, in an oven at 170 degrees. After 1 hour, I checked the internal temperature & calculated 3.6 hours total. 2 hours and 45 minutes after that, I checked again. (yes, I know .6 hours is 36 minutes; going a little over 156 degrees was better than not reaching 156 degrees, so I wasn't concerned about a few extra minutes). My meat thermometer showed about 157 degrees. WIN!


(oh, and it's delicious!! Just over 10 pounds of summer sausage.) Between the piles of jerky that we made, the summer sausage, and all the roasts, steaks, loins, and ground venison, I'm going to have some excellent food to eat this winter.